Welcome.
cp8759 deals mostly with council/decriminalised PCNs, but the rest of us can help you.
the registered keeper was my partner [...] It is my name on the paperwork
This suggests that some correspondence was exchanged with ECP by
someone at some point. That said, if you definitely were not the keeper of the vehicle, that makes the following statement in the particulars of claim even more ridiculous:
"In the alternative the defendant is pursued as the keeper pursuant to POFA 2012, Schedule 4"
Proof if ever it were needed that DCB Legal make absolutely no effort to check the details of the cases before wheeling out their standard wording.
You're correct that the next step is to acknowledge service. There is nothing to be gained by delaying the AoS. Follow the advice in this PDF on how to file the AoS:
https://www.dropbox.com/s/xvqu3bask5m0zir/money-claim-online-How-to-Acknowledge.pdf?dl=0When you have submitted the AoS, let us know.
A clear pattern has emerged with DCB Legal, especially with claims for single tickets, like this one, where as long as the case is defended, they eventually discontinue before the matter reaches a court hearing. For some background reading into this pattern, read the following:
DCB LEGAL RECORD OF PRIVATE PARKING COURT CLAIM DISCONTINUATIONS